1. Field of the Invention
The present invention relates generally to probe cards that are used to perform tests on semiconductor devices. The present invention more particularly relates to the cleaning of probe elements that extend from such probe cards.
2. Background Art
Individual semiconductor (integrated circuit) devices (dies) are typically produced by creating several identical dies on a semiconductor wafer, using known techniques of photolithography, deposition, and the like. Generally, these processes are intended to create a plurality of fully-functional integrated circuit devices, prior to singulating (severing) the individual dies from the semiconductor wafer. In practice, however, certain physical defects in the wafer itself and certain defects in the processing of the wafer inevitably lead to some of the dies being “good” (fully-functional) and some of the dies being “bad” (non-functional). It is generally desirable to be able to identify which of the plurality of dies on a wafer are good dies prior to their packaging, and preferably prior to their being singulated from the wafer. To this end, a wafer “tester” or “prober” may advantageously be employed to make a plurality of discrete pressure connections to a like plurality of discrete connection pads (bond or contact pads) on the dies. In this manner, the semiconductor dies can be tested and exercised, prior to singulating the dies from the wafer. A conventional component of a wafer tester is a “probe card” to which a plurality of probe elements are connected—tips of the probe elements effecting the pressure connections to the respective pads of the semiconductor dies.
More specifically, in the typical wafer testing process, the probe card is mounted to the prober, and probe elements (simply referred to as “probes”) extending from the probe card are brought into contact with pads formed on the dies of the wafer. In one process, electrical connection of the prober and the pads is achieved by applying a predetermined pressure to the probes after the probes have been brought into contact with the pads so that the probes penetrate the material forming the surface of the pads and come into low-resistance contact with the portions forming the bodies of the pads. Such penetration of the pad surfaces produces debris (e.g., aluminum oxide chips). In a more preferred process, used with probes that are elastic or springy, electrical connection of the prober and the pads can be achieved by applying a predetermined pressure to the springy probes after the probes have been brought in contact with the pads so that the probes are compressed, making a solid electrical connection. When the probes are compressed, a slight X and/or Y swipe is affected to the probes causing a portion of the material (e.g., an aluminum oxide film) forming the surface of the pads to be scraped off. The scraping of the pad surfaces produces debris (e.g., aluminum oxide chips).
Foreign matter including aluminum oxide chips (i.e., debris) adhering to the dies and/or the probes may obstruct proper electrical connection. Various measures have been taken to prevent problems in achieving satisfactory electrical contact.
In one conventional probe cleaning process, an abrading pad is used to remove foreign materials adhering to end portions (e.g., tips) of the probes. The abrading pad can be composed of a mixture of an elastic base material and abrasive particles. Alternatively, the abrading pad can be composed of tungsten carbide. Foreign materials adhering to the tips of the probes are scraped off the tips by repeating a cleaning cycle of pressing-and-extracting the tips of the probes against (and possibly into) the pad. The pressing-and-extracting cleaning cycle includes moving the abrading pad vertically (e.g., in the Z direction) against the probes, and then vertically away from the probes.
A disadvantage of the above described conventional cleaning process is that the portions of the base material (e.g., silicon rubber) and/or abrasive particles (e.g., abrasive grains) may fall or chip off the abrading pad during the pressing-and-extracting process, thereby producing additional foreign material that may stick to the probe tips. Further, foreign matter (previously removed from probe) that has fallen onto the abrading pad may later stick to the probes being cleaned. Accordingly, additional cleaning steps may be necessary to acceptably clean the probes.
These additional steps may include blowing an organic solvent against the probes, and then blowing dry air against the probes. The use of such solvents is undesirable for many reasons. For example, the blowing of an organic solvent is time consuming and potentially messy. Additionally, blowing of dry air is time consuming. Further, special equipment is required to blow the solvents and the dry air.
One attempt to improve upon the conventional process includes attaching a dust removing film to the top surface of the abrading pad. The purpose of the dust removing film is to confine foreign material, such as fine particles of worn base material and fallen abrasive particles produced by the repetition of the pressing-and-extracting cleaning cycle, so that those foreign materials may not be discharged outside the dust removing film. For example, this process may not be useful for cleaning elastic or springy contact probes (often referred to as “spring contacts” or “contact springs”), such as those disclosed in U.S. Pat. No. 6,184,053, entitled “Method of Making Microelectronic Spring Contact Elements,” U.S. Pat. No. 5,476,211, entitled “Method for Manufacturing Electrical Contacts, Using a Sacrificial Member,” U.S. Pat. No. 5,917,707, entitled “Flexible contact structure with an electrically conductive shell,” U.S. Pat. No. 6,110,823, entitled “Method of modifying the thickness of a plating on a member by creating a temperature gradient on the member, applications for employing such a method, and structures resulting from such a method,” U.S. Pat. No. 6,255,126, entitled “Lithographic contact elements”, and PCT Publication No. WO 00/33089, entitled ““Lithographic contact elements,” all of which are incorporated herein by reference.
Another attempt to improve upon the conventional probe cleaning process includes using a polymeric covered wafer to remove foreign materials following the pressing-and-extracting cleaning cycle described above. More specifically, the gel pad is positioned under the probes and then brought into contact with the probes (in a similar manner as the pressing-and-extracting using the abrading pad). The debris that has been loosened by the abrading pad, or produced by the abrading pad, sticks to the gel pad and is thereby removed from the probes. A disadvantage of this cleaning process is that an operator must typically swap the abrading pad with the gel pad during the cleaning process, because testing systems typically include only one auxiliary tray for holding such pads. This is undesirable because it prevents wafer testing from being a completely automated process, thereby significantly reducing wafer testing throughput.
Accordingly, there is a need for improved methods and apparatuses for cleaning probes.